Method and apparatus for cracking oil



n J. s. HARRISON f 1,767,360

METHOD AND APPARATUS FOR CRACKING OIL Filed March 26, .1927

J HN s. HARP 15 ON Patented June 24, 1930.

UNITED STATES PATENT orrlcs JOHN STEWART HARRISON, OF CLEVELAND, OHIO,ASS IGNOR TO STANDARD OIL DE- .V'ELOPMENT COMPANY, A CORPORATION OFDELAWARE METHOD AND APPARATUS FOR CRACKING OIL Application filed Ital-ch26, 1927. Serial No. 178,547.

This invention relates to improvements'i-n equipment and methods forhandling cracked hydrocarbon oil between the zones of crack- 'ing andfinal fractionation. I 1

The invention will be fully understood from the following descriptionread in connection with the accompanying drawing, in which the figure isa diagrammatic side elevation of a cracking plant comprising myimprovements.

Referring to the drawing, reference numeral 1 denotes a cracking coil ina furnace setting 2, and discharging through a pipe 3 into the lowerpart of an enlarged thermally insulated reaction chamber or soaking drum4. The cracking equipment itself is not a part of the present invention,and any approved type may be adopted.

The cracked product passes from near the top of the soaking drum 4through a pipe 5 into a tar separator 6. A pressure release valve 7 isinstalled in the pipe 5. A drawoff line 8 is connected to the separator,6 and leads to a tar cooler 9. Vapors pass' from the separator through apipe 10 to a perforated header 11 which is immersed ina body of liquidoil in an accumulator 12. Oil

to be cracked is supplied to the accumulator through a pipe 13. Thisincludes a heat exchange coil 14; arranged in the upper part of afractionating column or bubble tower 15.

A pipe 17 conveys vapors from the accumulator 12 to the bubble tower,preferably entering just above the bottom plate 18 therein. Thefractionated product passes from the tower through.a-pipe 19 to acondensing coil 20 and a'receiving drum 21. This latter has a vent pipe22 in which a pressure control valve 23 is installed.

Condensate formed in the tower and adapted for recycling is withdrawntothe accumulator 12 through pipe 24. The c'om-= bined liquid contents ofthe accumulator are forced by pump 25 through a pipe 26'to the v inletend of the cracking coil 1.

A pipe 27 connects the separator 6 and the accumulator 12. CA valve 28controls flow through this pipe. 'Valves 13' and'26 respectivelycontrol'flow through the pipes 13 i0 and'26. A pressure control valve10" may coil and drum being about 450 lbs; per square be installed inpipe 10. between the separator 6 and the accumulator 12.

The operation of the process willbe clear from the following example inwhich it is assumed that gas oil is to be cracked. The gas oil is pumpedthrough pipe 13 into accumulator 12 until the lever therein standsaboutas shown in the drawin The oil is then pumped from the accumu atorthrough pipe 26 into the cracking coil 1, which is suitably fired.During the cracking period the temperature of the oil at the outlet ofthe coil will be held at about 875 F, and in the drum at about 800 F.,the pressure in the inch.

The valve 7 will be set to give a pressure drop to about 60 lbs. gaugein the tar separator 6. This pressure is maintained throughout the restof the system by means of valve 23 on the receiving drum 21. In somecases it is desirable to maintain a higher pressure in the tarseparator, for example. 150 lbs. per square inch, though this may varywith the characteristics desired in the 7 tar product. The valve 10 maybe set to give the required pressure difl'erential between the tarseparator and the bubble tower.

: "The temperature of the tar in theseparater 6 will be about 67 5 F.,when working ,at 60'lbs. pressure, and the vapors emerge from theseparator at about the same tem-v perature. They impart their. heat tothe oil in the accumulator, which should be maintained at not less than550 F., as otherwise gasoline may be absorbed and retained by the gasoil supplied to the accumulator. At this temperature and 60 lbs.pressure, some kerosene, and perhaps light gas oil, will'pas's over withthe gasoline into the bubble tower. If it is desired to crack thekerosene and/or any heavier distillate fraction produced, this -may beseparately collected and returned to the accumulator or direct to thecracking coil. The temperature in thetar separator and the quality ofthe tar may be controlled by allowing more or less of the oil in. theaccumulator to flow into the separator through a pipe 27. w

"The present invention makes eflicient use 10 of the heating anddistilling efiect of the hot cracked product. High pressure heatexchangers are not required nor is the operation of the-bubble towerdisturbed by showering oil through it to obtain preheat, as hasheretofore been proposed. Further the accumula- 1 tor acts as astripping zone in which the heavier fractions of the cracked vaporscoming from the tar separator are condensed thus relieving the bubbletower and allowing it to. work in a more satisfactory manner.

It will be understood that the invention is not limited to operationupon the particular stock referred to, and that variations intemperature and pressure are permissible.

Numerous changes and alternative arrangements may be made within thescope of the appended claims in which it is my intention to claim allnovelty inherent in the invention as broadly as the prior art permits.

I claim:

1. Apparatus for cracking petroleum oil and separating gasolinetherefrom, comprising a cracking coil, a soaking drum in seriestherewith, a sole means for withdrawing cracked material from saidsoaking drum, means for reducing pressure thereon, a tar separator,means for conducting material withdrawn from said soaking drum underreduced pressure thereinto, means for withdrawing tar from saidseparator, means for withdrawing vapor from said se arator, anaccumulator having a normal liquid level therein, means for dischargingthe vapor withdrawn from said separator into said accumulator at a pointbelow the said normal liquid level, means for conducting vapors fromsaid accumulator, means for supplying oil thereto, means for conductingoil therefrom into the said cracking coil and a valved pipe connectingthe said tar separator with the said accumulator at a point below thenormal liquid level in the accumulator adapted to permit the transfer ofliquid from'the said accumulator into the said tar separator.

2. Process of cracking petroleum oil and separating a distillatetherefrom containing the cracked gasoline, which comprises heatingpetroleum oil to a cracking temperature by conducting same in a confinedstream througha heating zone, retaining the heated oil under pressure ina digestion zone, continuously withdrawing cracked hydro-carbon materialfrom the digestion zone in a single stream, discharging the stream ofcracked hydrocarbon material under reduced pressure and principally inthe vapor phase into a separating zone, separating tar therefrom andbubbling the remnant substantially tar free hydrocarbon vapors through abody of oil in a stripping zone under conditions adapted to partiallycondense said vapors while permitting a fraction containingsubstantially all the gasoline originally present in the said crackedhydrocarbon material Withdrawn from the digestion zone to remainuncondensed, rectifying the last mentioned uncondensed vapors in arectifying zone under conditions of partial condensation to produce acondensate and an overhead distillate containing substantially all thegasoline, continuously supplying feed oil to the stripping zone andcontinuously withdrawing oil therefrom and conducting the same throughthe heating zone in the confined stream first mentioned.

3. The process according to claim 2 in which the condensate obtained inthe rectifying zone is returned to the stripping zone.

4. The process according to claim 2 in which the temperature in theseparating zone and the quality of the tar are controlled by allowingoil to flow from the stripping zone to the separating zone in an amountnecessary or said control.

5. Process of cracking1 petroleum oil and separating a distillate terefrom containing the cracked gasoline, which comprises heatingpetroleum oil-to a cracking temperature by conducting same in a confinedstream through a heating zone, retaining the heated oil under pressurein a digestion zone, continuously withdrawing cracked hydrocarbonmaterial from the digestion zone in a single stream, discharging thestream of cracked hydrocarbon material under reduced pressure andprincipally in the vapor phase into a separating zone, separating tartherefrom and bubbling the remnant substantially tar free hydrocarbonvapors through a body of oil in a strippin zone under conditions adoptedto partia ly condense said vapors while permitting a fraction containingsubstantially all the gasoline originally present in the said crackedhydrocarbon material withdrawn from the digestion zone to remainuncondensed, continuously supplying feed oil to the stripping zone,Withdrawing oil therefrom and conducting the same through the heatingzone in the confined stream first mentioned and controlling thetemperature in the separating zone and the quality of the tar byallowing oil to flow from the stripping zone to the separating zone inan amount necessary for said control.

6. Apparatus for cracking petroleum oil and separating a distillatetherefrom containing the cracked gasoline, comprising a cracking coil, asoaking drum in series therewith, a sole means for withdrawing crackedmaterial from said soaking'drum, means for reducing pressure thereon, atar separator, means for conducting material withdrawn from said soakingdrum under reduced pressure thereinto, means for withdrawing tar fromsaid separator, means for withdrawing vapor from said separator, anaccumulator having a normal liquid level therein, means for dischargingthe vapor withdrawn from said separator into said accumulator at a pointbelow the said normal liquid level, means for supplying oil thereto, arectifying column, means for conducting vapors rom the accumulator intothe rectifying column, 5 cooling means in said column, means forconducting away vapors and means for conducting away condensate from therectifying column.

7. Apparatus according to claim 6 in 10 which the last mentioned meansare adapted for conducting the condensate from the rectifying columninto the accumulator.

JOHN STEWART HARRISON.

